Television transmitter



y 1941- I K.SCHLESINGER 2,248,548

TELEVISION TRANSMITTER Filed Aug. 2, 1935 3 Sheets-Shet l 7/? ran formag/w July 8, 1941. SCHLESINGER 2,248,548

TELEVISION TRANSMITTER Filed Aug. 2, 1935 3 Sheets-Sheet 2 July 8, 1941.K. scHLEsxNeER 2,248,548

I TELEVISION TRANSMITTER Filed Aug. 2, 1955 3 Sheets-Sheet 3 F 46 I I m;MM

. from the specification Patented July 8, 1941 2,248,548 TELEVISIONTRANSMITTER Kurt Schlesinger, Berlin, Germany, assignor, by

mesne assignments, to Loewe Radio, Inc., a corporation of New YorkApplication August 2, 1935, Serial No. 34,390 In Germany August 4, 19342 Claims.

The subject matter of the invention is a television transmission or amethod of scanning an original image, whereby the simultaneoustransmission of image signals and synchronisation signals takes place inparticularly simple fashion and of small cost with the use of one andthe same main amplifier. By way of explanation it is necessary to dealbriefly with the existing state of the television art.

An object of the invention is an arrangement for producingsynchronization impulses of constant peak potential.

Another object of the invention is an arrangement for producing saidsynchronization impulses by the scanning holes of the Nipkow disc.

Further objects of the invention will be seen in the accompanyingdrawings.

In the drawings,

Figure 1 shows diagrammatically an embodiment of a television filmtransmitter.

Figure 2 shows the course of the image potentials and synchronizationpotentials in the transmitter.

In Figure 3 there is illustrated a disc for scanning an image to betransmitted.

Figure 4 shows the size of the image projected on to the scanning discin comparison with the spacing between the scanning holes.

Figure 5 shows embodiments of a television film transmitter according tothe invention and Figures 6 and 7 show further forms of embodiments ofthe present invention.

In Fig. 1 an arc lamp I is used to intensely illuminate a film 3 by theuse of a condenser or hollow reflectorl, and the film image isreproduced on to to the Nipkow disc 5 by means of one or two lenses 4and 4'. If a photo-cell 6 with connected image amplifier l is placedbehind the Nipkow disc, preferably with the interposition of acollecting lens 8, there is available at the output of the image currentamplifier 1 the signalling potentials which correspond to the lightintensity values of the original film 3. No synchronisation impulses arepresent at the output of amplifier I.

The transmission is assumed to be a so-called positive transmission withblack synchronisation signals. A transmission of this kind isillustrated diagrammatically in Fig. 2. Although the invention describedin the following is not limited to a method of transmission of thiskind, the same will nevertheless be explained in conjunction with thediagram 2, as this method is becoming more and more popular. In Fig. 2the time t has been entered as abscissa and the aerial current i of thetransmitter as ordinate. As regards the transmission it is necessarythat the light intensity signals increase the aerial current in the caseof white and reduce it in the case of black, but even with extreme blackthe aerial current should not become zero. As a matter of'fact theentire current intensity interval between'a very white, 1. e.,transparent point of the film' anda point of the film completelyprecluding the transmission of light must be situated be tween twodefined limits, which are representedby the two broken horizontal lines9 and IE! for white and black. Complete choking of the aerial current isreserved to the synchronisation impulses, of which in Fig. 2 theshort-signal line impulses are represented by the curves II, and theimage-change impulse of greater duration by the curve l2. The separationof the synchronisation signals from the'image signal takes place in themanner known per se by an amplitude filter in the receiver. The latteris accomplished in the most simple manner by the use of a glow lamp.

In order to efiect transmission of synchronizing signals in practice inaccordance with Fig.2 there'has been provided a special'slot divisioningon the Nipkow disc of the transmitter (5' in Fig. l). A Nipkow disc ofthis kind, as shown in Fig. 3, is as follows:

On the outer periphery the apertures necessary for the scanning of theimage are arranged'in a circle, it being a condition that the film 3 iscontinuously advanced during the rotation of the disc. there isemployed, as well known, a disc having spirally disposed apertures. tionor image area I3 is selected of a size exactly corresponding with thespacing between two adjacent scanning apertures M. In order now toobtain the synchronisation signals, which were designated II and I2 inFig. 2, the disc 5 in Fig.1

3 requires a second divisioning. This consists of a ring of slots l5,which are lighted by a special light source IS (in Fig. l), and thelight transmitted through the slots are converted by means of a specialphoto-cell l1 and a special amplifier I8 into electrical synchronisationsignalsof constant intensity. Unfortunately the output potentials of theimage amplifier l and the syn chronisation amplifier l8 cannot merely besuperposed, as in this case the constant amplitude of thesynchronisation signals as set out in Fig. 2 would not be evenapproximately fulfilled. As a matter of fact there is required a specialappara- With intermittent movement of the film" The film reproducdiscwith special synchronisation slots as shown in Fig. 3 consists in thefact that the precision in the relative position of the slots l to theapertures I4 is never sufliciently good in practice, and that inconsequence a perfectly linear perpendicular line of the image is alwaysreproduced at the receiver with small curvatures. The

curvatures, to which the eye is very sensitive;

always occur when the precision in the position of the edge of a slot isless than the width of an image point. The particular line must thenobviously commencesomewhat too early ortoo late, so that the impression,i. e., the intensity modulation, is displaced in position on thereceived image in the order of magnitude of an image point as comparedwith the correct value. It is obvious that the electrical portion of thesystem cannot compensate for errors'in divisioning'of this kind. Thus,for example, even the filtering out of the synchronisation frequency byhighly selective apparatus, for example by tuning forks or by electricaltuned circuits, cannot assist'in straightening the perpendicular linesso that they may appear as if the image points have small dis placementerrors. x

The new method is illustrated in Fig. 5. The film optical system remainsthe same as in Fig. 1, and comprises the arc lamp l with the reflector2, the film 3, which is intended to run continuously, and preferably twolenses'4 and 4'. The film is assumed to be one of such brilliance thatthe light impinging on the Nipkow disc 5 com pletely disappears at theblack points, and is transmitted at the white points practically withoutweakening. Now the idea according to the invention consists inprojecting 'an additional uniform lighting over the field of thefilmimage on the disc 5 by a special auxiliary light source 23. Whilstthe film reproduction 24 as shown in Fig. 4, should be completelywithout light at the black points, the same, by means of the additionaluniform auxiliary lighting, is made brighter in homogeneous fashion overits entire width with an adjustable light intensity. According to theinvention, this additional lighting i projected over a width which isexactly the same in size as the width of the film image reproduction 24,i. e., auxiliary light and film light are caused exactly to register.The arouate portion of the disc for this lighting is,1however, shortenedby an interval 25 amountingto approximately 10% of the spacing betweentwo adjacent scanning apertures M. It will bequite obvious what occursnow in the photo-cell circuit B. It is assumed that the photo-cellcurrents are fully proportional to the light intensities behind thescanning aperture, and in particular theyshould reach their lowestvalue, or disappear, when the lighting entirely ceases. The primarylight through the lenses 4 and 4' will disappear even at the blackestpoints of the film reproduction. The secondary light, however, by

way of the lamp 23, the slot 3!, the selecting lens 2| and the deflectinprism 26, will continue to prevail also at these points, and thephoto-cell current will, therefore, not disappear during the entireimage. The two light sources I and. 23 are cut off only in the blackinterval 25. It is, therefore, only in this interval that the photo-cellcurrent becomes zero. If, as will be initially assumed, there isproportionality between intensity of light and aerial current throughoutthe entire transmitter, we obtain without further auxiliary apparatus ofany kind an aerial current diagram according to Fig. 2 with completeconstancy of the amplitudes of the synchronisation signals independentlyof the course of the image signals, and we can adjust by regulation ofthe light intensity of the lamp 23 by means of a series resistance 21the amount by which the synchronising signals exceed the maximum imageamplitudes. The brighter the lamp 23 is adjusted, the higher will be thepeaks II and I2 as compared with the interval 9 and I0 in Fig. 2.

By means of the described arrangement in Figs. 4 and 5 there is obtainedinitially merely the short line-change impulse H. the long image-changeor frame impulse l2 it is merely necessary in the case of a circularconcentrically apertured disc to allow a rotary diaphragm 28 to rotateat 25 periods per second. the frame frequency, and to arrange thisimmediately in front of the disc 5. With an opaque arm 29 thisdiaphragm, operated by means of a small synchronous motor 30, interceptsthe light from both light sources for the duration of approximately 5lines, so that during this absence of light there is obtained in thedesired fashion a disappearance of the photocell current 6 and, in thecase of the assumed proportionality, also of the aerial current 20.

The provision of a rotating diaphragm of this kind, which would notcause difficulties from a technical point of view, is renderedunnecessary by the use of a spiral aperture disc. When spiral aperturesare used it is possible to arrange a black image angle such as 25 inFig.4 also in a radial direction, i. e., the height of the lighted areamay be made smaller than the height of the radial divisioning in thespiral disc. In this way it may be accomplished that the-five extremeapertures pass over a surface which its adjusted to be completelywithout light. In this case the short and the long impulses II and I2 inFig. 2 will then be generated completely automatically. As well known,however, the arrangement with the circular concentrically apertureddisc, particularly in the case of a large number of lines, is superiorto the spiral disc.

Up to now it has been assumed that between the aerial current and thelighting of 6 there is a proportionality which is independent of theduration of the transmission of the signals, i. e.,

fication with condenser coupling true linearity cannot be accomplishedwithout resorting to additional compensating means, and thesynchronisation signals form under all circumstances a tangent to thezero lines of the aerial To producecurrent. If the subject matter in thefilm image persists at half-tone intensity for a comparatively lengthyperiod of time, the resistance-capacity coupled amplifier is unable toreproduce thev enduring lack of light, and its output potential inducesmerely weak potentials about the middle grey line. The difference in thephoto-cell current upon the passage of the aperture I 4 into the deadangle 25 is, however, merely very small, as the film image lightintensity at 24 was assumed itself merely to be very small, and thechange in light intensity corresponds in substance, therefore, to thecessation of the auxiliary lighting over the surface 24. In consequencethe synchronisation signals in this case do not reach the zero line ofthe aerial current. In a scene of this kind connected receiversnecessarily fall. In exactly analogous but reverse fashion an error insynchronisation makes itself noticeable upon the transmission of a filmscene taking place continuously in bright sunshine, since theresistance-capacity coupled amplifier is unable to reproduce thecontinuous presence of bright sunshine and records merely weakdifferences in intensity between more and less bright points in theoriginal, does not dispose these small oscillations, as should be thecase, about the maximum line 9 (Fig. 2) but instead they are disposedabout the middle grey line. In this case, however, the jump in lightingwhen the scanning aperture leaves the image surface 24 and enters thedead angle 25 is particularly great, as the photo-cell 6 registers notonly the omission'of the auxiliary light 23, but also in addition thedisappearance of the reproducing light, which in the case of the statedscene is very bright. Owing to the incorrect mean value. of theamplifier output potential, which is not situated at 9 but between 9 andI (Fig. 2), the synchronisation signals fall this time below the aerialcurrent minimum, assuming this to be possible at all.

If the aerial current is so adjusted that the same is reduced completelyto zero by the impulses in the case of normal signalling and normalintensity of the scene, more strongly throttling signals are unable todiminish the aerial current still further. Proper reduction of theaerial current is possible, however, even with the use of aresistance-capacity coupled amplifier if the auxiliary lighting isincreased in such fashion that even with a complete absence of imagelighting the change in the amount of light projected on the photo-cellbetween 24 and 25 in Fig. 4 is so large that in each case thetransmitting aerial current will with certainty disappear. There isaccordingly included a saturation limit at a desired point in thetransmission chain 7-20. Either the characteristic of the transmitter isso adjusted that the maximum fluctuation between black and white in theoriginal film image does not completely make full use of the range ofthe transmitter (current value 9 and I!) (Fig. 2), and the intensity ofthe auxiliary lighting 23 amplified to such extent that cessation of theauxiliary lighting alone is sufiicient in each case to completelyeliminate the aerial current, or a potential limitation of this kind isintroduced within the low-frequency amplifier I. It is only requiredthat the anode current of the final tube reach saturation, or that thegrid bias of the final tube, by the application of grid current or bythe use of a glow lamp particularly poor in capacity connected inparallel with the grid leak resistance of the final stage, with suitablebias, prevent an increase of the grid alternating potential in the finalstage beyond a maximum surge value. It is then accomplished that greatervalues than this potential limit do not occur, 1. e., that all impulsesreach the same absolute potential value, and by the increase in theauxiliary lighting as referred to above it is only necessary that thislimit is regularly attained upon scanning with the auxiliary lightingalone, i. e., in the absence of film lighting.

It may again be remarked that when using purely direct current coupledamplifiers, carrier frequency amplifiers and amplifiers with glow lampcoupling, i. e., with stationary proportionality of the photo-cell 6 upto the aerial 20 saturation conditions of this kind are unnecessary,andrelatively small auxiliary lighting 23 is sufficient, in addition towhich there is also the advantage that the medium intensity of the scenecan at least be reproduced in the aerial current. As regards thereceived image, however, this method of transmission results in noimprovement so long as the receiver does also not operate withoutcondensers and a stationary proportionality is provided between strengthof field and light intensity in the receiver. So long as the televisionreceiver operates with a condenser coupling in front of the receivinglight relay, use of the stated method of transmission cannot offeradvantages. In these cases useof the resistancecapacity coupledamplifier in conjunction with saturation effects and strong auxiliarylighting is of particular importance in practice, as theresistance-capacity coupled amplifier is very simple in assembly anduse.

The invention, which has been described in the above in conjunction witha perforated disc transmitter, may also be employed, however, quitegenerally. For example, it is quite readily possible to make use of thesame in transmitters where the subject matter transmitted originates ina studio rather than being derived from a film.

An arrangement for carrying-out the invention in practice in the case ofa cinema transmitter is illustrated by way of example in Fig. 6, saidarrangement containing in addition to the features set forth in theabove a particularly advantageous arrangement. for producing theauxiliary lighting.

In the same:

I is the arc lamp, this .beingthe only source of light occurring in thesystem. By means of the reflector 2 or condenser the light isconcentrated on to the film, the image to be transmitted on eachoccasion being represented by the section 3a. It'is assumed that thelight intensity of the image field is uniform over the entire picturearea 311, as may be expected in the kinematographic art.

Now the transmitter according to the invention is intended to operatewith a circular concentrically apertured disc- 5, which accordingly hasthe property of scanning merely one single line in the entire height ofthe image 3a; The image-3a is reproduced sharply on the disc 5 by meansof two lenses 4 and 4. The line 32 scanned by the disc 5 represents theonly line in the entire image which is utilised optically, and allremaining lines of the film are not embraced by the scanning operation.Accordingly the total remaining light on the picture area 3a is uselessfor the television transmission. On the other hand, as shown in theabove,a very considerable additional amount of light must be projectedon to'the film. reproduction 24 on the Nipkow disc, and this additionallighting must be approximately equal in amount to the lighting intensityof snowy white points in the original. In order to solve this problemwithout the heavy expense of a second arc lamp, as merely an arc lampcould supply the requisite intensity of light, it is very natural inaccordance with the invention to make use of the part of the light whichis not utilised for the scanning of the image and traverses the picture3a outside of the scanned line 32. For this purpose, in accordance withthe invention, the scanned line 32 is not, as hitherto usual, disposedat the centre of the image, but the line of the original reproduced onthe scanning disc is displaced in relation to the path of the bundle ofrays 33 and located at 32. This may readily be accomplished in practiceby lifting or lowering the entire projection apparatus together with thefilm 3 and the lenses 4 and 4', with respect to the position ofelevation of the axis of the Nipkow disc. The reproduction of the film24 is then lowered or lifted on the disc, and in this manner the edge ofthe reproduced image is practically made to register with the radiusdefined by the scanning apertures. Now in accordance with the invention,the following possibility is provided of rational utilisation of theremaining light:

' A deflecting prism 34, preferably one composed of durable glass (Ignalglass) projects that portion of the light which otherwise would impingeon the picture area 3a above the line 32 to be transmitted vertically tothe path of the reproducing rays. The part of the film 3, whichotherwise without a prism would be lighted, accordingly remains black.The rays impinge on a slot or mask 35, of which more particularly thewidth e requires to be reproduced sharply. Behind the slot or mask 35there is located a second deflecting prism 35. One or two lenses 31 and38 are provided, and then in turn two deflecting prisms 39 and 40. Thelast-mentioned prism is tilted to a somewhat greater extent, so that theauxiliary light, as required, covers the same area of the scanning disc5 as the reproduction of the original picture area 3a. The intensity ofthe auxiliary light may be adjusted in very simple fashion by an irisshutter provided for example at 4|, whereby the height of thesynchronizing impulse may be optically varied. If the maximum auxiliarylight intensity obtainable in this way is not sufficient, an additionalincrease in the auxiliary light may be efiected with the assistance of acondenser lens furnished at 42 by concentration of the light coming from34 on the slot or mask 35.

The form of embodiment set forth in Fig. 6 having one are lamp has theadditional advantage as compared with the stated arrangements having twoarc lamps in that the ratio between the original lighting and theauxiliary lighting is always maintained even upon fluctuations of I, andby means of an automatic regulating means for the common photo-amplifierwhich is usually provided in any case an error or variation of this kindon the amplifier side may be fully compensated.

The method of auxiliary lighting may be employed in simple fashion forautomatically regulating the degree of amplification according to thelighting intensity. For this purpose a part of the by-passed light, isdirected upon a white plate 43 positioned near and inclined with respectto the slot 35, and is reflected against a control photo-cell 44. Acrossthe load resistance 46 of the photo-cell 44 there is then developed apotential which is negative with respect to earth in proportion to theintensity of the arc lamp Therefore, if 41 is a tube in the train of themain amplifier behind the disc 5, this regulating potential may beconducted in the form of a bias to the control grid of the tube 41 byway of the line 48 in order to attain the desired effect and the maximumoutput potential is maintained constant independently of the lightingintensity, the sensitivity of the amplifier being increased upon adecrease in the illumination by the are I, and vice versa.

Further, in accordance with the invention, the amplification is soadjusted that (1) Only upon scanning such points of the original whichare as clear as'glass on the one hand, and points completely withoutlight on the other hand, at which the auxiliary lighting disappears, i.e., in the dead angle of the image, are the limits of the modulationcharacteristic of the transmitter reached.

(2) The aerial feed current is adjusted to that particular stationaryvalue, which upon passage hrough a black-and-white scale in the originalcorresponds with the grey value of this scale. This aerial feed currentis relatively high and amounts to approximately 60% of the maximumaerial current.

Another optical system for carrying out the method is shown in Fig. '7.This arrangement has the advantage that the same lenses which areemployed for reproducing the film also perform simultaneouslyre-reproduction of the light ing slot. There is again provided a lightsource l with a condenser reflector 2, and by means of a prism 34 alarge part of the light, which does not fall on to the scanned line 32,is deflected out of the main ray. As compared with Fig. 6, however, theby-passed light and the primary light are united before reaching thefirst lens 4. If the light proceeding from I has already been directedalong parallel paths by the hollow refiector 2, only a portion of thesurface of the lens 4 need be employed for reproducing the scanned line32, via, the part situated below the broken line 49. It is,therefore-possible without loss of light to unite the by-passed light 50with the primary light 5| in the lens 4 and to project and focus theimage of the slot or mask on the disc 5 provided the spacing 52 has beencorrectly adjusted. The slot or mask 35 is so adjusted with respect toits spacing 52 and the prism so rotated that the reflected image of theslot 35 is situated above the line 32. As well known, this is the casewhen the optical length 52 is equal to the length 52', and the base ofthe prism bisects the angle formed between the two. By means of adiaphragm 4| and a condenser lens 42 an improvement and quantitativeapportioning of the compound lighting may be obtained.

I claim:

1. A television transmission arrangement comprising a Nipkow disccontaining a row of scanning holes, a photoelectric cell, a singlesource of light, means including said source of light for projecting animage of the object to be transmitted onto said Nipkow disc, and meansincluding said source of light for projecting an additional light bundleupon the image projection onto said Nipkow disc, said additionallighting exactly covering the image field, the length of said imagefield being smaller than the spacing between said scanning holes, andmeans for producing an image current in said photoelectric cell byscanning said image field, an electronic amplifier for amplifying saidimage currents, a light responsive element, said light responsiveelement being positioned to receive light from the single source inproportion to the intensity of the source to produce a voltageproportional to the light intensity, and means to control theeffectiveness of the electronic amplifier by the produced voltagewhereby the strength of the amplified image currents will besubstantially unailected by changes in the intensity of the source oflight.

2. A television transmission arrangement comprising a Nipkow disccontaining a row of scanning holes, a photoelectric cell, a singlesource of light, means including said source of light for projecting animage of the object to be transmitted onto said Nipkow disc, and meansincluding said source of light for projecting an additional light bundleupon the image projection onto said Nipkow disc, said additionallighting exactly covering the image field, the length of said imagefield being smaller than the spacing between said scanning holes, andmeans for producing an image current in said photoelectric cell byscanning said image field, an electronic amplifier for amplifying saidimage currents, means responsive to the light from the source forproducing a potential substantially proportional to the intensity of thesingle source of light, and means for controlling the image currentamplifier by the produced potential whereby the strength of theamplified image current will be substantially unaffected by changes inthe intensity of the single light source. I

KURT SCHLESINGER.

